MCHW Vol 2 Ng5700 Feb 2020
MCHW Vol 2 Ng5700 Feb 2020
MCHW Vol 2 Ng5700 Feb 2020
SERIES NG 5700
CONCRETE REPAIRS
Contents
Clause Title Page
NG 5701 (02/20) Concrete Repair – Introduction 2
NG 5702 (02/20) Concrete Repair Work –
General Requirements 3
NG 5703 (02/20) Products and Systems for Repair
of Concrete Structures – General 4
NG 5704 (02/20) BS EN 1504 Part 3 Products for
Concrete Repair 6
NG 5705 (02/20) Supply and Storage of
Proprietary Repair Products and Other
Materials 7
NG 5706 (02/20) Contractor Investigation 7
NG 5707 (02/20) Pre-Construction Concrete
Repair Execution Trials 8
NG 5708 (02/20) Quality Control of Repair Work 8
NG 5709 (02/20) Concrete Removal 10
NG 5710 (02/20) Substrate Preparation 14
NG 5711 (02/20) Reinforcement 14
NG 5712 (02/20) Galvanic Anodes for Control
of Incipient Anode Effect 16
NG 5713 (02/20) Falsework and Formwork 18
NG 5714 (02/20) Site Mixing, Placing, Finishing
and Curing 19
NG 5715 (02/20) Flowable Concrete or Mortar 20
NG 5716 (02/20) Repair Concrete or Mortar 21
NG 5717 (02/20) Sprayed Concrete or Mortar 22
NG 5718 (02/20) Repairs to Structures to Receive
Impressed Current Cathodic Protection 25
NG 5719 (02/20) Repairs to Structures using
Galvanic Anodes for Control of Incipient
Anode Effect 26
NG 5720 (02/20) Concrete Injection 27
NG 5721 (02/20) Contract Compliance Testing on
Completed Repairs 28
CONCRETE REPAIRS
4 (02/20) The specification of surface protection systems for concrete (products defined in BS EN 1504 Part 2)
and for structural bonding (products defined in BS EN 1504 Part 4), are not covered by Series 5700. Use of those
systems currently requires the preparation of specification AR Clauses for consideration by the Departure from
Standards approval procedure.
5 (02/20) Neither Series 1700 nor this Series 5700 cover new construction using sprayed concrete e.g. sprayed
concrete facing to cast in-situ concrete piles, or sprayed concrete as a new tunnel lining, additional specification AR
Clauses should be prepared for consideration by the Departures from Standard approval procedure. BS EN 14487
Part 1 may be used for advice on specifying designed mix sprayed concrete.
6 (02/20) Where a designed mix flowable concrete is proposed for planned large area or anticipated repairs of
decks, the mix should be designed in accordance with Series 1700 to achieve similar performance characteristics to
BS EN 1504 Part 3 products. Testing will be needed to demonstrate required performance can be achieved before
construction, and to prove compliance following casting. Describe testing in Appendix 17/4 and schedule in
Appendix 1/5 or 1/6 (see sub-clause NG 1727.1).
7 (02/20) Repairs to concrete carriageways are outside the scope of Series 5700. Refer to HD 32 (DMRB 7.4.2)
and Clauses 1032 and 1033).
8 (02/20) The compiler should use Series 1700 to specify lightweight concrete.
(02/20) BS EN 1504 Terms and Definitions
9 (02/20) BS EN 1504 provides manufacturers of repair products with a framework for obtaining certification for
their repair products under the terms of the Construction Products Regulation.
10 (02/20) Definitions, requirements, quality control and evaluation of conformity for products and systems
intended for repair of concrete may be found in:
(i) BS EN 1504 Part 1 – definitions;
(ii) BS EN 1504 Part 3 – structural and non-structural repair products;
(iii) BS EN 1504 Part 5 – concrete injection;
(iv) BS EN 1504 Part 6 – anchoring of reinforcing steel bar; and,
(v) BS EN 1504 Part 7 – reinforcement corrosion protection.
11 (02/20) The BS EN 1504 parts listed above are performance specifications and provided the required minimum
performance of essential characteristics specified in the relevant standards is achieved by a product, the
manufacturer is free to use different constituent materials in the formulation.
12 (02/20) BS EN 1504 Parts 2 and 4 are also used for manufacturing products but are not part of the scope of this
Series 5700 concrete repair specification.
13 (02/20) General terms and definitions useful for understanding the contents of BS EN 1504 are given in Part 1,
and more specific terms and definitions may be found in Parts 3, 5, 6, 7, 8, 9 and 10.
3 (02/20) The Contractor will be required to prepare technical approval documentation as necessary for temporary
support of structural members or temporary access to repair areas. See Clause 106, Clause NG 5713 and BD 2
(DMRB 1.1.1).
4 (02/20) If there are unusual site-specific constraints on the design of temporary works required to facilitate
construction of the works, the compiler should complete contract specific Appendix 1/11.
(02/20) Protection of Vulnerable Elements
5 (02/20) Concrete repair construction activities may include high pressure water jetting and sprayed concrete
which involve propelling liquids and solid particles at high velocity. Structure fixtures required for the safe
operation or articulation of the structure could be vulnerable to damage, so should be protected before commencing
work.
(02/20) Method Statements
6 (02/20) The compiler should ensure that contract specific Appendix 1/24 includes a list of topics for which the
Contractor is required to provide detailed method statements for concrete repair activities. This should be limited to
those where the method of construction, the design and/or the equipment to be used are crucial to the success of the
works or innovative.
7 (02/20) For acceptance the method statements should provide assurance that:
(i) safety risks have been adequately assessed, structural integrity is not compromised, and the proposed
method includes sufficient hazard mitigation; and,
(ii) proposed repair products and construction techniques are appropriate for the scope of work.
Some reasons for not accepting the documents are that:
(iii) they are inadequately prepared or not practicable;
(iv) they do not include the information specified;
(v) the approach is not realistic.
NG 5703 (02/20) Products and Systems for Repair of Concrete Structures – General
(02/20) Assessment and Verification of Consistency of Performance
1 (02/20) System of Attestation of Conformity referred to in Annex ZA.2 of BS EN 1504 Parts 3, 5, 6 and 7 was
replaced by an Assessment and Verification of Consistency of Performance (AVCP) when the Construction
Products Directive was replaced by the Construction Products Regulation in 2013. Standards published before
July 2013 refer to the former.
(02/20) Suitability of Construction Products
2 (02/20) A manufacturer of concrete repair products refers to BS EN 1504 Part 3 for the procedure to formally
identify products and obtain certification (CE marking) prior to placing them on the market for use in the
construction industry. The essential characteristics of repair products are assessed by testing and the manufacturer
declares their performance by a Declaration of Performance, and places CE marking on the products. Product
manufacturers are legally responsible for performance of CE marked products.
3 (02/20) Historically, contract specifications included requirements for controlling the risk of Alkali Silica
Reaction being activated by the component materials of concrete repair mixes. The control is now achieved before
those components are used by repair product manufacturers via product standards e.g. BS EN 12620, BS 8500
Part 2.
4 (02/20) The compiler should complete two tables of information in contract specific Appendix 57/1.
First table
Specifies mandatory performance characteristics of the repair products required for the works:
(i) Strength class of repairs. BS EN 1504 Part 3 strength R Class should be specified. The Contractor will
use the specified strength class and Table 57/1 in the specification to indicate which set of performance
requirements should be fulfilled by his choice of repair product;
(ii) Fire class of repairs. Where an assessment of the possible exposure to fire of concrete repairs in a
location has identified a reasonably significant risk of fire damage, or when fire resistance is required
by a design code of practice, the compiler should specify a fire class in contract specific Appendix 57/1.
See BS EN 13501 Part 1 for information about construction product fire classes;
(iii) Flowability of fresh repair material. Where a flowable concrete is or may be required, the flowability
of the repair material may be classed as high or normal flow (see definition in 5715 and suggested
application in NG 5715);
(iv) Minimum compressive strength or repair product. For repairs to some existing concrete elements,
even the highest class R4, may not guarantee an adequate compressive strength and a minimum
compressive strength should be specified in addition to “R4” listed in the first table of contract specific
Appendix 57/1. A value should only be specified if required compressive strength is greater than
50 MPa.
Second table
This should be populated with further information to assist the Contractor in his choice of BS EN 1504 Part 3 repair
product:
(i) Assumed compressive strength of existing concrete. This value can either be the original designed
compressive strength, the compressive strength given on as-built drawings, or compressive strength of a
tested core taken from the element to be repaired;
(ii) Assumed static modulus of existing concrete in tension or compression if appropriate. The contract
specification should aim to match the declared elastic modulus of a proposed sprayed concrete product
to the measured or estimated elastic modulus of the existing concrete to limit shear stresses at the
interface. It is important that the elastic modulus of a repair matches the estimated short-term elastic
modulus of the parent concrete for locations subject to frequent cycles of transient loading. It is
particularly important for structural members that are predominantly subjected to compressive forces in
service e.g. columns. The modulus of elasticity of the proposed concrete repair product should be within
a range approximately the same modulus up to +10 GPa of that estimated or measured for the existing
concrete;
(iii) Requirement for galvanic anodes within repair patches. Following completion of a designer assessment
of corrosion risk to reinforcement located in the existing intact but contaminated concrete surrounding
repairs as part of the design process (see BA 35), the compiler should indicate whether galvanic anodes
located within the repair patch are required;
(iv) Range of electrical resistivity of parent concrete. A concrete repair product may be marketed as
‘compatible for use with cathodic protection systems.’ BS EN ISO 12696 has a general recommendation
that repair products should have a resistivity within the range 50 – 200% of the parent concrete. The
compiler should include an assumed electrical resistivity of the parent concrete in contract specific
Appendix 57/1. Further guidance may be found in Technical Notes on the website of the Corrosion
Prevention Association (www.corrosionprevention.org.uk);
(v) Minimum strength of concrete repair patches before loading. Early strength gain for repairs to the deck
of a highway bridge. This may be relevant where the allowable road/lane closure is of short duration, or
where stages of repair are required to maintain structural stability.
5 (02/20) The compiler should refer to NG 5711 and NG 5720 for guidance about what information is required in
contract specific Appendices 57/2 and 57/5.
6 (02/20) If the compiler wishes to declare a future intention to overlay proposed repairs with a cathodic
protection system anode embedded in a cementitious layer, details of this should be included in contract specific
Appendix 57/3.
NG 5705 (02/20) Supply and Storage of Proprietary Repair Products and Other Materials
(02/20) Supply Data
1 (02/20) There is currently no product standard covering manufacture of galvanic anodes and reference
electrodes for use in reinforced concrete, so the manufacturer/supplier will be expected to confirm in writing that
the product complies with specification requirements.
(02/20) Marking and Labelling of Products
2 (02/20) Containers of the product delivered to site should have been CE marked in accordance with the relevant
standard.
Product containers should be marked with a declaration similar to “this product shall be deemed to comply with
BS EN 1504 Part 3 until (date)”.
3 (02/20) CE marking identifies repair products complying with BS EN 1504, but galvanic anodes and reference
electrodes are not covered by a harmonised standard and should be marked to identify the manufacturer, type and
unique reference.
(02/20) Storage
4 (02/20) Repair products are susceptible to deterioration, particularly when they are exposed to moisture, so it is
essential that they are stored properly in accordance with BS EN 1504 Part 10 and the manufacturer’s
recommendations.
Sometimes it is appropriate for the Overseeing Organisation to undertake a concrete condition survey during the
contract by making use of the Contractor’s traffic management. It may also be possible for the whole of a survey to
be assigned to the Contractor and the results provided to the Overseeing Organisation in the form of a report for
consideration and assessment of the extent of repair required. This option should only be used as a last resort
because without the survey information, the design cannot be finalised in advance of construction, and could result
in contact programming complications with a possible significant increase in costs.
The Contractor investigation will typically include a concrete defect survey (indentations, cracking, delamination),
measurement of concrete cover, electrical potential mapping (using a half cell testing instrument), chloride
sampling, cement content, carbonation tests and concrete resistivity testing. The location of measurements should
be on a specified regular grid (see advice in BA 35). Locations for testing should be shown on the drawings,
alternatively the compiler should describe principles for establishing the survey grid in contract specific
Appendix 57/6.
In some cases, it may be necessary to take chloride samples within the delaminated area if there is concern that
chlorides may have migrated further into the concrete since the most recent investigation was undertaken. Cores to
measure chloride content should be particularly targeted in areas where chloride contamination is expected or
known to have occurred, for example locations where potholes in bituminous surfacing have been regularly
recorded, and adjacent to deck movement joints.
2 (02/20) Advice about the extent of the concrete condition survey and the format and contents of the survey
report may be found in BA 35 (DMRB 3.3.2).
3 (02/20) The compiler should ensure that the timescale for supply of the concrete investigation report is stated in
contract specific Appendix 1/13. The time constraints should include a period for Overseeing Organisation to
review the report. The time periods should be appropriate for the contract specific programming constraints.
(ii) inspection of the repair area substrate after it has been prepared to confirm compliance with the
specification; and,
(iii) measurements and observations of ambient weather conditions.
Quality control is required initially before the first batch of fresh material is placed into position, and during
placement activities, to indicate consistency of the material and to confirm it has complied with the strength
requirements of the specified class.
2 (02/20) The compiler should refer to the list of typical sampling and testing requirements for concrete repair
work listed in Series NG 100, Table NG 1/1, and draw up a specific list for Contractor routine quality control and
contract compliance. The list should be included in contract specific Appendix 1/5.
Options include:
(i) Flowability (flowable repair materials). Flowability tests to confirm that mixed material complies with
the specification, indicating that the correct amount of water has been added and mixing has been carried
out effectively. (Reference BS EN 1504 Part 10. Annex A.5.4. Test No. 27);
(ii) Air content (flowable repair materials). Air content test is included to control the site mixing procedure.
Too high an air content could reduce concrete strength. (Reference BS EN 1504 Part 10. Annex A.5.4.
Test No. 28); and,
(iii) 28-day compressive strength (all materials). Tests for compressive strength on hardened concrete
specimens (cubes, prisms) at various ages will provide a good indication of the overall strength in the
hardened condition and indicate when the repair is strong enough to carry load. (Reference BS EN 1504
Part 10. Annex A.5.4. Test No. 36).
(02/20) Identity Testing by the Overseeing Organisation – Immediately before and/or during Placement of
Material
Table NG 57/1 (02/20) Typical Quality Control Testing by the Overseeing Organisation
The depth of concrete removal should usually be to at least 25mm behind the rear face of existing reinforcement, to
ensure the repair concrete has an adequate key into the structure. The minimum depth of removal behind
reinforcement may be reduced to 15mm where existing reinforcement is particularly congested but should not be
less than 2 ½ times the nominal maximum aggregate size of the proposed repair product, to ensure the space behind
reinforcement can be adequately filled. If the extent of concrete removal is not shown on the construction drawings,
the breakout extent should be described in contract specific Appendix 57/3.
Sometimes parts of a structure are temporarily supported to relieve loading on elements that are weakened by
removal and replacement of concrete.
The compiler should ensure that contract specific Appendix 57/3 is completed with a value for minimum strength
of new concrete before removal of temporary supports and reloading. The value should cross reference to contract
specific Appendix 57/1.
2 (02/20) Concrete removal often involves high pressure water jetting and grit blasting, and both construction
activities have the potential to damage adjacent elements of the structure. The compiler should include any
requirements for protection of vulnerable areas or other structural features in contract specific Appendix 57/3.
3 (02/20) All hazardous materials known or suspected to be present within the parts of the structure specified for
removal or anticipated as requiring removal should be brought to the Contractor’s attention. The compiler should
add a schedule of hazardous materials, locations and any particular special requirements for handling or disposal in
contract specific Appendix 1/23 whilst leaving the Contractor to establish safe systems of work, e.g. asbestos and
relevant information from the Asbestos Action Plan Risk Register. (This would be in addition to the compiler’s and
designer’s obligations under the Construction Design and Management Regulations).
(02/20) Pre-Breakout Survey (Contractor)
4 (02/20) Often there will be a time interval of months and sometimes years between the most recent concrete
condition survey, and repair work starting on site.
A pre-breakout survey is required by the Contractor before the repair works commence to identify if and where
areas of defective concrete have increased since the previous survey, to ensure that all delaminated concrete is
replaced. The pre-breakout survey is usually undertaken jointly with the Overseeing Organisation.
The structural implications of removing defective concrete from a concrete substructure element which is usually
subjected to compressive loading should be carefully considered. Adverse structural effect could be mitigated by
phasing of the repair work, by propping of the superstructure or by a temporary restriction of traffic loading.
Concrete removal in a tension zone could overstress the existing exposed reinforcement because anchorage length
is reduced, and bars may also be corroded.
If additional concrete defects are identified during a pre-breakout survey that are a significant increase to the extent
or depth of the original proposals, an addendum to the original technical approval for the structures may be
required.
(02/20) Procedure for Concrete Removal
5 (02/20) The Contractor is responsible for complying with the contract, and sometimes no further control on
concrete removal activities is considered necessary. The designer or compiler should identify areas of the structure
where removal of contaminated/defective concrete could be critical to the stability and hence safety. Technical
approval of the contractor’s proposals may be required.
If closer control of progress on concrete removal is required, further constraints should be added to contract
specific Appendix 57/3.
Aspects to consider for inclusion in contract specific Appendix 57/3 could include notification periods, inspection
and recording of the substrate, certification and progression to the next stage of breakout and any related hold
points for inspection and certification by the Contractor or Overseeing Organisation.
One example of a procedure is indicated below, but this should be modified to suit the extent of control to be
exercised, type of repairs known or anticipated, the extent of repairs and the relationship between the contracting
and supervising parties as dictated by the form of contract:
(i) Where defective concrete has been removed in a repair area to the depth and extent required by the
contract, the entire substrate in the repair area shall be hammer sounded. If there are any areas of hollow
sounding concrete they shall be marked out and the Overseeing Organisation shall be notified;
(ii) The Contractor shall notify the Overseeing Organisation at least <x> hours before requiring an
inspection, provide suitable access and allow a period of <x> hours for the recording and inspection;
(iii) Following inspection, the Contractor shall not proceed to the next stage of repair until the Overseeing
Organisation has confirmed <by a communication method> either that:
(a) extent of breakout is accepted, and work may proceed; or,
(b) extent of breakout is unacceptable and further breakout is required prior to re-inspection; or
(c) additional breakout is specified prior to a further inspection.
(iv) The Contractor shall not remove additional concrete until the designer has confirmed the structure
capacity will be adequate or whether additional temporary supports are required; and,
(v) Where the existing concrete from a specified repair area has been removed in accordance with the
contract documents, additional breakout has been carried out, the substrate has been hammer sounded
again, and the reinforcement has been cleaned in accordance with sub-Clause <x>, the Contractor shall
notify the Overseeing Organisation of an intention to proceed to the next stage of repair.
6 (02/20) Where repairs to the top surface of concrete decks are anticipated, during replacement of existing deck
waterproofing, it is often helpful to define the extent of treatment to superficial defects in sound concrete, e.g.
hollows, peaks, boot marks, significant cracking, previous road planer damage etc. This may help avoid delays in
construction during lane closures of short duration. Note that where delamination of concrete is caused by
reinforcement corrosion, repairs to behind reinforcement should always be carried out.
Some guidance on the acceptability of the existing deck surfacing for application of waterproofing may be found in
TRL Published Project Report PPR 376
The compiler should define the general procedure for dealing with superficial defects in contract specific
Appendix 57/3.
(02/20) Sequencing of Concrete Removal
7 (02/20) The structural implications of removing defective concrete from a concrete substructure element which
is usually subjected to compressive loading should be carefully considered. There is a risk of reducing the
pre- stressing forces in a pre-tensioned concrete member during removal of concrete.
Adverse structural effect could be mitigated by phasing of the repair work, by propping of the superstructure or by
a temporary restriction of traffic loading. Concrete removal in a tension zone could place too much reliance on the
existing exposed reinforcement which may also be corroded.
While in some cases it may be possible to extend the size of the current repair to deal with all corroded
reinforcement, this will not always be the case and the structural implications of further breakout should be
considered. Where necessary a further stage in the repair sequence should be added.
If concrete removal and replacement needs to be carried out in stages to avoid weakening and overloading a
structural element, sequencing restrictions should be described in contact specific Appendix 57/3.
(02/20) Particular Requirements of Concrete Removal
8 (02/20) During concrete breakout, corroding reinforcement may be found to extend beyond the edge of the
repair. Breakout should be extended to expose 100mm of uncorroded reinforcement.
9 (02/20) The primary purpose of a concrete repair is to restore the protective surround to reinforcing bars now
lost due to chloride contamination and concrete delamination. However, the appearance of completed repair patches
is also a relevant consideration. The perimeter of a concrete repair patch should be made up of a small number (at
least 4 no.) of straight edges to form a regular shape.
(02/20) Post-Breakout Substrate Inspection
10 (02/20) The post breakout inspection provides an opportunity for a works supervisor to confirm that the removal
of concrete in identified repair areas is proceeding satisfactorily and provides feedback to the operatives that
workmanship is acceptable.
(02/20) Methods of Removing Defective Concrete
(02/20) General
11 (02/20) Trials were undertaken in 1989 investigating different techniques of concrete removal. High pressure
water jetting was shown as the best technique for removal of concrete at a reasonable rate leaving a competent
substrate which would provide a good bond to the repair concrete without the use of bonding agents.
High pressure or ultra-high-pressure water jetting has become popular for using in preference to mechanical
breakout, because there is much smaller risk of damaging the remaining concrete by introducing micro cracking.
Break out using mechanical tools can cause micro cracking and create a weak layer or potential failure plane
immediately below the broken-out surface. This is also known as concrete bruising.
12 (02/20) The risk of introducing micro cracking into pre-stressed or post-tensioned concrete members should be
avoided, and defective concrete in these elements should be removed using high pressure water jetting.
13 (02/20) Other methods of concrete demolition e.g. concrete sawing, concrete removal by laser, are highly
specialised processes and details of such a method are required to be prepared and submitted to the Overseeing
Organisation as a departure from standard.
(02/20) High Pressure Water Jetting
14 (02/20) Water jetting is a potentially dangerous construction activity. The consequences of an accident to an
operative when using high pressure water jetting can be severe. There is also a risk of significant overbreak if the
operations are not carefully controlled. It is therefore essential that it is undertaken by operatives with appropriate
qualifications, training and experience.
(02/20) Disposal of Waste
15 (02/20) Water arising from the concrete removal by high pressure water jetting will contain particulates, and its
pH will be high. As the water sprayed at high pressure comes into contact with the concrete, the pH of the water
may increase up to a value of 13 which is too high for discharge to a watercourse. The water, particulates and debris
should be collected, treated and disposed of in an appropriate way.
Causing or allowing pollution of watercourses is a criminal offence and could result in prosecution. Environmental
good practice guidance may be found in the Guidance for Pollution Prevention (GPPs) on the NetRegs website
(www.netregs.org.uk). This guidance is applicable in the whole of the UK.
Environmental regulatory guidance for construction work in England may be found on GOV.UK website (www.
gov.uk). Regulatory guidance for work in Scotland, Northern Ireland and Wales may be found in the GPPs.
Contaminated water may be treated on site to remove contamination (e.g. particulates and high pH), and
subsequently discharged to a foul sewer, however the Contractor should obtain from the relevant environmental
regulator or water authority prior consent to the water cleaning process and method. The Overseeing Organisation
should expect to see details of such consent before the Contractor is permitted to commence disposal.
4 (02/20) The cement content of modern-day cementitious repair products is often much higher than used in a
typical 1960s concrete. If the design indicates that the existing reinforcement cannot cope with the risk of increased
shrinkage forces and early thermal cracking due to anticipated high cement content of the repair concrete, the
compiler should add a schedule of additional bar or mesh reinforcement to contract specific Appendix 57/2.
Refer to CIRIA C660/C766 for a guide to providing reinforcement to resist early thermal cracking.
New reinforcement should be made of carbon steel to match existing. Stainless steel is not generally permitted
because of the risk of bimetallic corrosion particularly in the splash zones where corrosion has occurred previously.
(02/20) Reinforcement Couplers
5 (02/20) Reinforcement couplers should be made of carbon steel to be compatible with existing reinforcement.
Reinforcement coupler fatigue capacity must be suitable for the applied stress range and number of expected
occurrences (cycles) of that stress range during the remaining life of the structure. For fatigue sensitive locations,
couplers tested and certified to a minimum of fatigue Class D should be specified. Details of couplers certified to
Class D or better are published on the CARES (www.ukcares.com) or British Board of Agrément (www.bbacerts.
co.uk) websites.
Steel couplers are generally designed for splicing modern metric bar sizes. If couplers are to be used with old
imperial sizes and more modern metric diameters, the coupler manufacturer should be consulted about whether the
mix of sizes would affect certified strength properties.
The compiler should add in contract specific Appendix 57/2 any contract specific requirements for reinforcement
couplers e.g. reinforcement diameters (if known), fatigue class and areas where couplers would not be acceptable
because concrete cover could be compromised.
(02/20) Splicing Replacement or Additional Reinforcing Bars
6 (02/20) Wherever possible, replacement reinforcement should be lapped. Reinforcement couplers in accordance
with Clause 1716 may also be considered, but adequate concrete cover should be provided.
Reinforcement lap lengths and nominal cover should be indicated in contract specific Appendix 57/2.
7 (02/20) Welding of replacement bars may be desirable because of space restrictions.
Design of welded joints should also be checked against the requirements of Clause 3.2.5 of BS EN 1992-1-1,
before specifying.
Butt welding of reinforcement is the preferred method, but if this cannot be achieved, fillet welding may be
acceptable provided welded bars are proposed in non-fatigue prone areas of the structures. Any proposals for fillet
welding in fatigue prone locations (reference BS EN 1992-1-1) should be subject to fatigue verification assessment.
If welding of reinforcing bars is shown to be acceptable, the compiler should specify welding requirements in
contract specific Appendix 57/2.
The contract compiler should include in contract specific Appendix 1/5, any requirement for pre-construction
welded test pieces to prove competence of welders, and non-destructive testing of the permanent welds on site.
8 (02/20) Contractor proposals for welding should be checked for compliance with Clause 1717 and particularly
Clause 3.2.5 of BS EN 1992-1-1.
(02/20) Anchoring of Reinforcing Bars and Dowels
9 (02/20) Where it is not practicable to remove sufficient existing concrete to completely encompass existing
reinforcement (e.g. repairs to impact damaged pre-stressed beams), or when adhesion provided by the concrete
substrate is considered inadequate for the applied interface stresses in service (e.g. extensive and superficial repairs
to a concrete deck), additional reinforcement dowels may be provided across the interface to resist in-plane
stresses. See EOTA Technical Report TR 29.
This method of securing a repair using anchored reinforcement or dowels should not be used instead of the
preferred repair solution i.e. replacing concrete to behind the outermost reinforcement to achieve a good
mechanical key for the repair.
If dowels are to be anchored into a structural element subject to fire requirements, the compiler should specify a
reaction to fire classification in contract specific Appendix 57/2.
6 (02/20) Reference electrodes should remain useable for at least 20 years, and during that time it should be
possible to reliably interrogate the system potential or corrosion current. Readings should remain stable regardless
of variations in concrete temperature. More information can be obtained from BS EN ISO 12696 (monitoring
sensors).
(02/20) Acceptance of Products
7 (02/20) Galvanic anodes are proprietary products. Their manufacture is not currently covered by a British
Standard or British Standard Euronorm. As a result, the Contractor is required to provide evidence of the quality of
the manufacturing process; evidence that the proposed anode has performed satisfactorily in service, and examples
of installations where the product has achieved the minimum life required by the contract without premature
delamination of concrete adjacent to the repair.
(02/20) Contractor Design
8 (02/20) Where the Contractor is required to design the galvanic anode system, the compiler should specify this
in contract specific Appendix 1/10, and cross reference to contract specific Appendix 57/7.
The compiler should include in the contract appropriate supporting information e.g. the existing reinforcement
drawings, concrete testing reports. The minimum free chloride content of the adjacent existing concrete, and
maximum reinforcement density to be assumed in the design should be specified in contract specific
Appendix 57/7.
9 (02/20) Where a longer service life than 10 years is required, the compiler should specify this in contract
specific Appendix 57/7.
10 (02/20) Where permanent reference electrodes are required, the compiler should specify requirements in
contract specific Appendix 57/7.
(02/20) Products and Materials
The compiler should also show on a contract drawing, details of any reinforcement required in the test panel. The
type number and spacing of bars should be representative of a typical part of an element to be repaired.
Studs or screws should be cast into the test panel so that shrinkage can be measured later.
Stainless pins are cast in to measure electrical resistivity where required.
Where repairs are required to many similar structural elements e.g. pier bents, and the pattern of defects to each
bent is similar, it might be appropriate to specify construction of a miniature model of an element, and for the
Contractor to demonstrate repair technique on that. The mock-up model could be used instead of sprayed concrete
test panels to demonstrate operator workmanship and is currently referred to in Clause NG 5707.
(02/20) Samples to be Removed from Test Panels
9 (02/20) The compiler should specify in contract specific Appendix 57/4 and contract specific Appendix 1/5 the
samples to be removed from the sprayed concrete test panels. Typical sampling is indicated in Table NG 57/2
below.
Table NG 57/2 (02/20) Typical Examples of Concrete Samples to be Removed from Sprayed Test
Panels.
No. of samples or measurement and For testing or measurement of
Type of sample
type of panel which performance characteristic?
Core through reinforcement (100mm 4 no. samples from 1 no. reinforced test Integrity – containing minimal air
dia.) panel voids and no shadowing behind bars
3 no. samples from each of 2 no. plain test
Core (50mm or 100mm dia.) 28-day compressive strength
panels
3 no. samples from each of 2 no. plain test
Core (50mm or 100mm dia.) 28-day elastic modulus (secant)
panels
1 no. measurement set from each of 3 no.
Studs or screws in-situ on test panels Percentage shrinkage at 28 days
plain and reinforced test panels
3 no. samples from one or more plain test
150mm cube cut from panels Electrical resistivity at 28 days
panels
(ii) Testing for compressive strength and elastic modulus. The cores taken from the panels may be
destructively tested to determine the following performance characteristics when the concrete is 28 days
old:
(a) compressive strength;
(b) elastic (secant) modulus.
Where a sprayed product (concrete or mortar) is specified, it may be important that the Elastic (secant)
Modulus of hardened sprayed concrete is broadly matched to that of the existing concrete. This could be
relevant when concrete is required to restore a cross section which is partly or completely subjected to
compressive forces and required to act compositely under variable loading;
(iii) Testing for shrinkage. The concrete shrinkage will be monitored in the concrete remaining in the test
panels for a period of four weeks to confirm the operative’s skill. A further shrinkage measurement at
56 days will be required;
(iv) Testing for electrical resistivity. The electrical resistivity of the sprayed concrete when the concrete
is 28 days old. This test would only be required if the design included galvanic anodes within repair
patches or impressed current CP system within an overlay is proposed as part of the contact or planned
for a later date.
(02/20) Test Result Acceptability Criteria
13 (02/20) If a cathodic protection system is planned to be installed over the sprayed concrete repairs as part of the
contract or in the future, the compiler should include in contract specific Appendix 57/3 brief details and if
available, the type and form of CP system (see also NG 5718).
(02/20) Quality Control – Assessment of Conformity
Resin based repair mortars are not suitable for use in conjunction with electrochemical treatments, neither are repair
products containing conductive additives, admixtures or fibres. This is because current flow associated with the
cathodic protection is interrupted by the high resistivity of resin and current defection of additives, admixtures and
conductive fibres, and adversely affects the protection of reinforcement.
(02/20) Removal of Detrimental Objects and Old Repairs
3 (02/20) Metallic objects embedded and visible within the surface concrete e.g. tying wire, nails, formwork tie
bars, unfixed reinforcing bar etc., are likely to interfere with and adversely affect the protective current flowing as
part of the cathodic protective system. They should be identified, and a detail of how they should be treated shown
on the drawings. The compiler should include a list of elements where embedded objects have been identified in
contract specific Appendix 57/3.
If resistivity of an existing concrete repair patch exceeds 100 kΩ•cm, the voltage of an impressed current cathodic
protection system may not be able to drive the protective current through the repair to the reinforcement. If the
resistivity of an existing concrete repair is higher than permitted, and a cathodic protection system is proposed, the
compiler should schedule these in contract specific Appendix 57/3.
(02/20) Testing of Completed Repairs
4 (02/20) The resistivity of completed repairs should not be so high it impedes current flow from an impressed
current cathodic protection system applied over the top. The compiler should indicate an estimated range of
electrical resistivity of the existing concrete in the second table of contract specific Appendix 57/1 (Reference
BS EN 1504 Part 10. Annex A.5.4. Test No. 15).
5 (02/20) Guidance on testing of concrete for electrical resistivity may be found in Electrochemical Tests for
Reinforcement Corrosion published by the Concrete Society/Institute of Corrosion and Measurement of Concrete
Resistivity for Assessment of Corrosion Severity of Steel using Wenner Technique from the ACI Journal published
by the American Concrete Institute.
NG 5719 (02/20) Repairs to Structures using Galvanic Anodes for Control of Incipient Anode
Effect
(02/20) General
1 (02/20) Concrete repair product may be marketed as compatible for use with cathodic protection systems.
2 (02/20) Galvanic anodes generate their own current and drive voltage which is much smaller than an ICCP
system. The galvanic current needs to draw chloride ions from the existing concrete just outside the repair patch
towards the anodes.
Using a high resistivity repair product for repairs may significantly reduce current flow. The specification includes
a range of acceptable electrical resistivity.
Resin-based repair mortars are not suitable for use in conjunction with electrochemical treatments; neither are
repair products containing conductive additives, admixtures and fibres (e.g. steel or carbon fibres). This is because
current generated by galvanic anodes is impeded by the high resistivity of polymer resin and current deflection is
caused by conductive fibres. This reduces the amount of protection to reinforcement.
(02/20) Testing of Completed Repairs
3 (02/20) BS EN ISO 12696 has a general recommendation that repair products should have a resistivity within
the range 50 – 200% of the parent concrete, however galvanic anodes generate a limited drive voltage, so a limited
resistivity of the repair concrete is more important for galvanic anode systems. The range of acceptable electrical
resistivity is based on the advice given in Technical Note 19 of the Corrosion Prevention Association (part of the
Structural Concrete Alliance).
4 (02/20) Published guidance on testing of concrete for electrical resistivity may be found in Electrochemical
Tests for Reinforcement Corrosion and Measurement of Concrete Resistivity for Assessment of Corrosion Severity
of Steel using Wenner Technique.
5 (02/20) Tables 57/6, 57/7 and 57/8 are based on Tables 6, 7 and 8 of BS EN 1504 Part 5. The tables have been
sub-divided for of the two common classifications of binder (H and P) used for formulating the products. Binder
types are defined in the standard.
(02/20) Inspection to Identify Cracks for Treatment
6 (02/20) Where the Contractor is required to carry out a survey of concrete cracking, the compiler should specify
details in contract specific Appendix 57/5.
(02/20) Quality Control Tests
7 (02/20) The compiler should specify routine quality control tests in contract specific Appendix 1/5, with
reference to Table NG 1/1 in Series NG 100.
(02/20) Preparation of Cracks
8 (02/20) BS EN 1504 Part 10, Annex A.8 contains advice about techniques of concrete injection. Moisture within
a crack may be pre-existing or introduced during cleaning. It should be removed prior to filling of cracks. Hot air
may be used for this, and a method using nitrogen gas could also be considered.
(02/20) Execution of Concrete Injection
9 (02/20) BS EN 1504 Part 10, Annex A.8 contains advice about techniques of concrete injection. Further
information and guidance may be found in Concrete Society publication TR 69, Repair of Concrete Structures with
reference to BS EN 1504.
Concrete injection should be carried out by an appropriate method that ensures complete filling of the crack. If the
proposed method includes combined vacuum and pressure, injection pressures will generally be limited to a
positive pressure of 1.5 bar combined with a vacuum negative pressure not greater than –0.75 bar.
(02/20) Contract Compliance Tests
10 (02/20) The frequency of contract compliance testing should be indicated in contract specific Appendix 1/5, with
reference to Table NG 1/1 in Series NG 100.
The compiler should specify the frequency and distribution of cores in contract specific Appendix 57/3 and should
refer to Table NG 1/1 in Series NG 100 to complete the required testing schedule in contract specific Appendix 1/5.
(02/20) Cores – Injection/Filling of Cracks
8 (02/20) Coring through filled cracks will provide evidence that the injected product has filled the cracks. If the
extent of crack filling is not acceptable, cores can be loaded in compression to destruction as further test.
The compiler should describe the general location for cores in contract specific Appendix 57/5 and should refer to
Table NG 1/1 in Series NG 100 to complete the required testing schedule in contract specific Appendix 1/5.
The existing reinforcement should be located and marked before deciding where to drill the core holes (Reference
BS EN 1504 Part 10. Annex A.5.4, Observation No. 33).
(02/20) Adhesion to Substrate
9 (02/20) BS EN 1504 Part 10, Annex A.5.2, Table A.2 suggests values for adhesion strength of repair mortar. The
compiler should specify target adhesion strength for each location in contract specific Appendix 57/3.
(02/20) Compressive Strength
10 (02/20) Compressive strength of tested samples should be greater that required by the BS EN 1504 Part 3
strength class of proprietary products, specified in contract specific Appendix 57/1.
(02/20) Filling or Injecting of Cracks
11 (02/20) It is normal for the repair industry to specify that cracks being injected should be filled at least 80% full
by volume. If the compiler considers that a higher percentage is necessary for a scheme, this may be specified in
contract specific Appendix 57/5. It is unlikely that cracks can be 100% filled.
If the cores taken through filled cracks show that they are not filled adequately, the cores may be further assessed
for acceptability by compression testing to determine adhesion strength between the hardened injection material
and the parent concrete (Reference BS EN 1504 Part 10. Annex A.5.4. Test No. 44).
3 (02/20) Contract specific information provided to assist Contractor in choice of repair product. [5703.2(i),
5703.5(i), Table 57/5, 5717.16, NG 5718, 5721.3, 5721.11]
Description of structure Compressive Static elastic Galvanic Range of Minimum
and/or structural element strength of modulus of anodes electrical strength of
existing existing required within resistivity of repair concrete
concrete being concrete in repair patches? parent concrete before loading
repaired. tension (T) or permitted.
compression
(C)
# x φ ♠ Ђ
(MPa) (MPa) (Yes/No) (Ω•cm) (MPa)
SPRAYED CONCRETE
[Note to compiler: Requirements for proprietary sprayed concrete products should be specified in terms of product
classes in accordance with Clause 5704.2.]
1 (02/20) Requirement for a particular sprayed concrete application process i.e. dry-spray or wet spray. [If not
completed the Contractor will be free to choose.] [5717.3]
2 (02/20) If a wet-spray application process is specified, the required consistence of the mix in accordance with
BS EN 206. [5717.6, 5717.19]
3 (02/20) Different requirements for size of sprayed concrete test panels. [5717.9]
4 (02/20) Required inclination of each pre-works sprayed concrete test panels. [5717.9]
5 (02/20) Samples to be removed from the pre-works sprayed concrete test panels for later testing. [5717.9]
6 (02/20) Inspection category if not BS EN 14487 Part 1, Category 3. [5717.21]
7 (02/20) Alternative requirements for formation of construction joints. [5717.24]
8 (02/20) Description and specification of alternative to as-sprayed concrete finish. [5715.26]
CONCRETE INJECTION
[Note to compiler: Include here the following contract specific requirements and details:]
1 (02/20) Required concrete crack repair method for each structural element reference BS EN 1504 Part 9
(Principle 1, method 1.5, Principle 4, method 4.5 or Principle 4, method 4.6). [5702.1]
2 (02/20) Schedule of characteristics for each crack or group of similar cracks to be injected (structure
identification, element reference, location, length, minimum thickness). Example shown below. [5703.5, 5720.3,
Table 57/6]
Structure ID Structural Location No of crack Range of crack Minimum Maximum
element defects length (mm) width of width of crack
type crack (mm) (mm)
e.g. Bridge A Beam 4 East end 3 300 – 600 0.25 0.75
3 (02/20) The function each injection product should perform – force transmitting filling, ductile filling or
swelling-fitted filling in accordance with BS EN 1504 Part 5 should be tabulated for each defect to be treated under
references for individual defects or set of defects grouped under a structural element reference number. Example is
shown in the table below. [5703.2 (iii), 5720.3, 5720.4, Table 57/6, Table 57/7, Table 57/8]
Function of injection product Force Ductile filling Swelling fitted
transmitting (D) filling (S)
filling (F)
(Basic
Performance requirement (Basic (Workability
characteristic)
characteristic) characteristic)
Adhesion by
Adhesion Expansion ratio
Structural No of crack tensile bond strength ** **
Structure ID Location strength *
element type defects
(N/mm2) (%)
(F1 or F2)
e.g. Bridge A Beam 2 North end 3 F2 – –